[DT-2775] Improve Data Submission Error Messaging

[kevinmarete]

Addresses

https://broadworkbench.atlassian.net/browse/DT-2775

Summary

This PR and the (UI part) improve submission validation errors so users can easily understand what’s missing and where to fix it. Instead of showing internal schema paths and raw validation output, error messages now use user-facing field names.

After.mov

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Have you read CONTRIBUTING.md lately? If not, do that first.

• Label PR with a Jira ticket number and include a link to the ticket
• Label PR with a security risk modifier [no, low, medium, high]
• PR describes scope of changes
• Get a minimum of one thumbs worth of review, preferably two if enough team members are available
• Get PO sign-off for all non-trivial UI or workflow changes
• Verify all tests go green
• Test this change deployed correctly and works on dev environment after deployment

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
84.3% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud